Ground-state Hyperfine Levels Research Articles

Anomalous to normal dispersion nonlinear optical dephasing switch in electromagnetically induced transparency using a Kerr effect

The atomic decoherence effect (DE) on a Kerr nonlinear (KNL) electromagnetically induced transparency (EIT)is studied in a Δ system. The DE between the ground state hyperfine levels is caused by the dephasing rate γ d which dramatically modifies the medium response. It controls the normal dispersive region which shows steep positive slopes for linear response at the line center while the nonlinear response experiences steep negative slopes for low γ d . The microwave field strength and γ d modify the nonlinear response from the anomalous dispersion to normal dispersion. The calculations show that room-temperature atoms are used to quantify the quantum interference (QI) on linear and nonlinear absorption with γ d . The EIT spectrum explores the understanding of the subluminal and superluminal wave propagation of probe signal and this study opens a new pathway for the understanding of the QI devices and their nonlinearities based on EIT.

Hyperfine transition induced by atomic motion above a paraffin-coated magnetic film

We measured transitions between the hyperfine levels of the electronic ground state of potassium-39 atoms (transition frequency: 460 MHz) as the atoms moved through a periodic magneto-static field produced above the magnetic-stripe domains of a magnetic film. The period length of the magnetic field was 3.8 µm. The atoms were incident to the field as an impinging beam with the most probable velocity of 550 m s−1 and experienced a peak oscillating field of 20 mT. Unwanted spin relaxation caused by the collisions of the atoms with the film surface was suppressed by the paraffin coating on the film. We observed increasing hyperfine transition probabilities as the frequency of the field oscillations experienced by the atoms increased from 0 to 140 MHz for the atomic velocity of 550 m s−1, by changing the incident angle of the atomic beam with respect to the stripe domains. Numerical calculation of the time evolution of the hyperfine states revealed that the oscillating magnetic field experienced by the atoms induced the hyperfine transitions, and the main process was not a single-quantum transition but rather multi-quanta transitions.

Mixed-field effect at the hyperfine level of 127I79Br in its rovibronic ground state: Toward field manipulation of cold molecules

The mixed-field effect at the hyperfine level of the rovibronic ground state of the 127I79Br (X1Σ, v = 0, J = 0) molecule is computed on the J–I uncoupled basis of |JMJI 1 M 1 I 2 M 2〉, where J is the molecular total angular momentum excluding nuclear spin, MJ is the projection number of J, I 1 and I 2 are the nuclear spins of the iodine and bromine atoms, and M 1 and M 2 are the projection numbers of I 1 and I 2, respectively. When the two applied electric and magnetic fields are parallel, the perturbations are rare and only one perturbation is observed in a relatively large field regime in our computation range. However, when the two fields are off-parallel, the perturbations increase significantly and some sublevels show the Feshbach-like resonance phenomenon. Therefore, such sublevels transit between weak-field seeking and strong-field seeking repeatedly, which can be utilized to enhance or suppress cold molecular collision and chemical reaction rates. Such behavior of the molecular hyperfine structure in the mixed off-parallel fields may also be utilized to construct an electric-field-assisted anti-Helmholtz magnetic trap for cold molecules and to realize evaporative cooling of cold molecules (sub-mK) into the ultracold regime (μK).

Observation of Narrow Optical Homogeneous Linewidth and Long Nuclear Spin Lifetimes in a Prototypical [Eu(trensal)] Complex

Coherent light–matter interfaces are key elements for many quantum information processing architectures. Rare-earth ion (REI)-containing systems featuring narrow inter-configurational f–f transitions are suitable for creating such interfaces. Recently, narrow homogeneous linewidths (Γh) and long nuclear spin lifetimes (T1spin) associated with two Eu3+ complexes featuring the 5D0 → 7F0 f–f transition have been reported, elucidating that REI-molecule-based coherent light–matter interfaces can be obtained. In this study, we report a homogeneous linewidth of 2.8 MHz at 4.2 K, corresponding to an optical coherence lifetime (T2opt) of 114 ns (0.11 μs), associated with the 5D0 → 7F0 transition of the prototypical charge neutral Eu3+ complex─[Eu(trensal)]. Moreover, we have observed long nuclear spin lifetimes (T1spin) up to 460 ± 80 s at 4.2 K for the complex and efficient optical pumping of hyperfine levels of the 5D0 ground state. The results presented in this study indicate that narrow homogeneous linewidths and long nuclear spin lifetimes could be a generic property of molecular Eu3+ complexes featuring the 5D0 → 7F0 transition.

Microscopic model of spin flip-flop processes in crystals doped by rare-earth ions

Flip-flop processes due to magnetic dipole-dipole interaction between neighboring ions in crystals doped by rare-earth ions are one of the mechanisms of relaxation between hyperfine levels. Modeling of this mechanism has so far been macroscopic, characterized by an average rate describing the relaxation of all ions. Here, however, we present a microscopic model of flip-flop interactions between individual nuclear spins of dopant ions. Every ion is situated in a unique local environment in the crystal, where each ion has different distances and a unique orientation relative to its nearest neighbors, as determined by the lattice structure. Thus each ion has a unique flip-flop rate and the collective relaxation dynamics of all ions in a bulk crystal is a sum of many exponential decays, giving rise to a distribution of rates rather than a single average decay rate. We employ this model to calculate flip-flop rates in ${\mathrm{Pr}}^{3+}$:${\mathrm{Y}}_{2}{\mathrm{SiO}}_{5}$ and show experimental measurements of population decay of the ground state hyperfine levels at $\ensuremath{\sim}2$ K. We also present a method to measure rates of individual transitions from hole burning spectra that requires significantly fewer fitting parameters in theoretical rate equations compared to earlier work. Furthermore, we measure the effect of external magnetic field on the flip-flop rates and observe that the rates slow down by two orders of magnitude in a field of 5--10 mT.

Effects of spin-exchange collisions on the fluctuation spectra of hot alkali-metal vapors

We present a first-principles analysis of the noise spectra of alkali-metal-metal vapors in and out of the spin-exchange-relaxation-free (SERF) regime, and we predict non-intuitive features with a potential to further improve the sensitivity of SERF media, and which must be taken into account in their use in quantum optical applications. Studying the process of spin-noise spectroscopy (SNS), we derive analytic formulas for the observable noise spectra, and for the correlation functions among different hyperfine components, which give additional insight into the spin dynamics. The analytic results indicate a variety of distortions of the spin-noise spectrum relative to simpler models, including a broad spectral background that mimics optical shot noise, interference of noise contributions from the two ground-state hyperfine levels, noise reduction at the spin-precession frequency, and ``hiding'' of spin-noise power that can introduce a systematic error in noise-based calibrations, e.g., for spin-squeezing experiments.

A compact gain-enhanced microwave helical antenna for 87Rb atomic experiments.

We present a compact and gain-enhanced microwave helical antenna for manipulating ultracold 87Rb atoms coherently. By replacing the reflecting plate with an enhancing cup, the voltage standing wave ratio is reduced by 0.5 in the frequency range of 6.73-6.93GHz, which covers the resonant frequency between the ground-state hyperfine levels of the 87Rb atom. The gain of the helical antenna is increased by 1.25-1.63 dBi, whose length is 89mm. Applying the antenna to ultracold 87Rb atomic experiments, we achieve a Rabi frequency of 60(1) ×2π kHz of the oscillation between the hyperfine levels.

Proposal for a Deterministic Single-Atom Source of Quasisuperradiant N-Photon Pulses.

We propose a single-atom, cavity quantum electrodynamics system, compatible with recently demonstrated, fiber-integrated micro- and nanocavity setups, for the on-demand production of optical number-state, 0N-state, and binomial-code-state pulses. The scheme makes use of Raman transitions within an entire atomic ground-state hyperfine level and operates with laser and cavity fields detuned from the atomic transition by much more than the excited-state hyperfine splitting. This enables reduction of the dynamics to that of a simple, cavity-damped Tavis-Cummings model with the collective spin determined by the total angular momentum of the ground hyperfine level.

High-temperature lithium atomic magnetometry by symmetric hyperfine coherent population trapping resonances

A glass lithium vapor cell is an atomic sensor operating at high temperature. The longitudinal magnetic-field strength is measured by coherent population trapping (CPT) in ground-state hyperfine levels. Two linearly polarized light beams are polarized orthogonally to each other. The difference of optical frequencies is tuned to generate a dark state. Additionally, a few light modes of equidistant frequency spacing are generated by modulating the difference frequency. The symmetry of the light modes and the energy levels enables simultaneous measurement of the hyperfine splitting frequency of the ground state and the magnetic-field strength. Tuning the optical frequency difference to the central CPT resonance, a sensitivity of 15 p T / H z is achieved. The time response and the sensitivity of the CPT magnetometry are studied by changing the cell temperature, the laser power, the frequency separation of the light modes, and the Zeeman frequency.

Assembly of a Rovibrational Ground State Molecule in an Optical Tweezer.

We demonstrate the coherent creation of a single NaCs molecule in its rotational, vibrational, and electronic (rovibronic) ground state in an optical tweezer. Starting with a weakly bound Feshbach molecule, we locate a two-photon transition via the |c^{3}Σ_{1},v^{'}=26⟩ excited state and drive coherent Rabi oscillations between the Feshbach state and a single hyperfine level of the NaCs rovibronic ground state |X^{1}Σ,v^{''}=0,N^{''}=0⟩ with a binding energy of D_{0}=h×147044.63(11) GHz. We measure a lifetime of 3.4±1.6 s for the rovibronic ground state molecule, which possesses a large molecule-frame dipole moment of 4.6D and occupies predominantly the motional ground state. These long-lived, fully quantum-state-controlled individual dipolar molecules provide a key resource for molecule-based quantum simulation and information processing.

Search for topological defect of axionlike model with cesium atomic comagnetometer* *Project supported by the National Natural Science Foundation of China (Grant No. 62071012), the National Science Fund for Distinguished Young Scholars of China (Grant No. 61225003), and National Hi-Tech Research and Development Program of China.

Many terrestrial experiments have been designed to detect domain walls composed of axions or axionlike particles (ALPs), which are promising candidates of dark matter. When the domain wall crosses over the Earth, the pseudoscalar field of ALPs could couple to the atomic spins. Such exotic spin-dependent couplings can be searched for by monitoring the transient-in-time change of the atomic spin precession frequency in the presence of a magnetic field. We propose here a single-species cesium atomic comagnetometer, which measures the spin precession frequencies of atoms in different ground-state hyperfine levels, to eliminate the common-mode magnetic-field variations and search for the exotic non-magnetic couplings solely between protons and ALPs. With the single-species atomic comagnetometer, we experimentally rule out the possibility that the decay constant of the linear pseudoscalar couplings of ALPs to protons is f p ≲ 3.71 × 107 GeV. The advanced system has the potential to constrain the constant to be f p ≲ 10.7 × 109 GeV, promising to improve astrophysical constraint level by at least one order of magnitude. Our system could provide a sensitive detection method for the global network of optical magnetometers to search for exotic physics.

Coherent manipulation of the internal state of ultracold 87Rb133Cs molecules with multiple microwave fields.

We explore coherent multi-photon processes in 87Rb133Cs molecules using 3-level lambda and ladder configurations of rotational and hyperfine states, and discuss their relevance to future applications in quantum computation and quantum simulation. In the lambda configuration, we demonstrate the driving of population between two hyperfine levels of the rotational ground state via a two-photon Raman transition. Such pairs of states may be used in the future as a quantum memory, and we measure a Ramsey coherence time for a superposition of these states of 58(9) ms. In the ladder configuration, we show that we can generate and coherently populate microwave dressed states via the observation of an Autler-Townes doublet. We demonstrate that we can control the strength of this dressing by varying the intensity of the microwave coupling field. Finally, we perform spectroscopy of the rotational states of 87Rb133Cs up to N = 6, highlighting the potential of ultracold molecules for quantum simulation in synthetic dimensions. By fitting the measured transition frequencies we determine a new value of the centrifugal distortion coefficient Dv = h × 207.3(2) Hz.

Theoretical analysis of the coupling between Feshbach states and hyperfine excited states in the creation of 23Na40K molecule**Project supported by the National Key Research and Development Program of China (Grant No. 2018YFA0306502), the National Natural Science Foundation of China (Grant Nos. 11521063 and 11904355), and the Fund from the Chinese Academy of Sciences (CAS).

We present an intensive study of the coupling between different Feshbach states and the hyperfine levels of the excited states in the adiabatic creation of 23Na40K ground-state molecules. We use coupled-channel method to calculate the wave function of the Feshbach molecules, and give the short-range wave function of triplet component. The energies of the hyperfine excited states and the coupling strength between the Feshbach states and the hyperfine excited states are calculated. Our results can be used to prepare a specific hyperfine level of the rovibrational ground state to study the ultracold collisions involving molecules.

Microwave Pulse-Coherent Technique-Based Clock With a Novel Magnetron-Type Cavity

We report a high-performance pulsed optically pumped (POP) Rb clock based on a novel magnetron-type microwave cavity. The cavity has a volume of 30 mL, enabling a highly homogenous microwave field distribution. With the laser frequency tuning to the ground-state hyperfine level F = 2 of the D2 line, we observe a Ramsey fringe contrast of 52% in terms of optical absorption detection. The resultant shot noise limit is estimated to be [Formula: see text]. The clock frequency stability is measured as [Formula: see text] (1-100 s), which is limited by the relative intensity noise of the light.

Transmission spectroscopy of a single atom in the presence of tensor light shifts

We investigate the interplay between Zeeman and light shifts in the transmission spectrum of an optically trapped, spin-polarized Rubidium atom. The spectral shape of the transmission changes from multiple, broad resonances to a single, narrow Lorentzian with a high resonant extinction value when we increase the magnetic field strength and lower the depth of the dipole trap. We present an experimental configuration well-suited for quantum information applications that enables not only efficient light-atom coupling, but also a long coherence time between ground state hyperfine levels.

Measurements of spin properties of atomic systems in and out of equilibrium via noise spectroscopy.

We explore the applications of spin noise spectroscopy (SNS) for detection of the spin properties of atomic ensembles in and out of equilibrium. In SNS, a linearly polarized far-detuned probe beam on passing through an ensemble of atomic spins acquires the information of the spin correlations of the system which is extracted using its time-resolved Faraday-rotation noise. We measure various atomic, magnetic and sub-atomic properties as well as perform precision magnetometry using SNS in rubidium atomic vapor in thermal equilibrium. Thereafter, we manipulate the relative spin populations between different ground state hyperfine levels of rubidium by controlled optical pumping which drives the system out of equilibrium. We then apply SNS to probe such spin imbalance non-perturbatively. We further use this driven atomic vapor to demonstrate that SNS can have better resolution than typical absorption spectroscopy in detecting spectral lines in the presence of various spectral broadening mechanisms.

Practical method for transversely measuring the spin polarization of optically pumped alkali atoms

A practical method to measure the spin polarization of optically pumped alkali atoms is demonstrated. In order to realize transverse measurement, the transverse spin component of spin-polarized alkali atoms is created by a rotating exciting magnetic field, and detected using the optical rotation of a near-resonant probe beam for realizing a high detection sensitivity. The dependency of the optical rotation on the spin polarization of 133Cs atoms is derived theoretically and verified experimentally. By changing the direction of the rotating magnetic field, we realize the transverse measurement of the spin polarization of 133Cs atoms in either ground-state hyperfine level.

Selective excitation of spin-polarized alkali atoms in different ground-state hyperfine levels

A technique to selectively excite spin-polarized alkali atoms in one of the two ground-state hyperfine levels is demonstrated, which can separately create the transverse spin component of spin-polarized alkali atoms in either ground-state hyperfine level. The principle of this technique is analyzed, and the experimental results are found to be in good agreement with the theoretical predictions, thereby demonstrating the feasibility of this technique. This technique can be used to accurately measure spin relaxation and polarization of alkali atoms in either ground-state hyperfine level. An example of its applications to measure the transverse relaxation time is presented.

Influence of optical pumping on the transverse spin relaxation of Cs atoms in different ground-state hyperfine levels

The influence of optical pumping on the transverse spin relaxation of 133Cs atoms in different ground-state hyperfine levels is investigated. Transverse relaxation times for 133Cs atoms in the two ground-state hyperfine levels are detected separately under different intensities and frequencies of pump light, and a statistical model is adopted to analyze the experimental results. Theory and experiment show that optical pumping changes the populations of the two ground-state hyperfine levels, thereby influencing the transverse spin relaxation due to spin-exchange collisions. As a result, an unusual phenomenon that the transverse relaxation time for 133Cs atoms in the upper ground-state hyperfine level increases with the pump-light intensity is observed.

Zeeman Effect of the Rovibronic Ground State of I35Cl at Hyperfine Level

Zeeman effect at the hyperfine level of the rovibronic ground state of I35Cl are determined on the basis of via an effective Hamiltonian matrix diagonalization method. Perturbations of the Zeeman sublevels are observed and the perturbation selection rules are summarized as well. Several potential applications of such Zeeman effect are suggested.